This invention relates to a method of heat treating amorphous alloy ribbons, and more particularly, to a method of heat treating amorphous alloy ribbons to uniformly enhance the magnetic properties of the amorphous alloy ribbons, while maintaining the noncrystalline character of the amorphous alloy ribbons.
Recently, thin films of amorphous alloys have been found to be quite useful for technological purposes, and commonly, manufactured through a method in which the melted liquid-alloy is first forced through nozzle means and then, ejected onto a high speed rotating body so as to be instantly quenched thereon.
However, with the above-described method including the so-called splat cooling step, the resultant film formed in a long strip, or more particularly, the amorphous alloy ribbon, generally lacks uniformity with respect to its product-dimensions as well as the specific properties thereof.
As far as the magnetic property is concerned, further proposals to uniformly enhance the magnetic properties of the amorphous alloy ribbons manufactured by the method mentioned above have been proposed.
For example, U.S. Pat. No. 4,053,333 discloses a method for increasing the residual magnetic flux density of the ribbons of nickel based amorphous alloys through a process including the steps of subjecting the ribbons mentioned above to a tensile stress in the range of 20 to 40 kg/mm.sup.2, and successively, heating the ribbons mentioned above at a predetermined temperature below the specific melting point or, preferably, in the vicinity of 200.degree. C., for a predetermined duration.
However, the heat-annealing mentioned above can be performed by accommodating the ribbons in an annealing furnace and thereby, maintaining the alloys therein for more than several minutes.
It is, however, to be noted here that, when the ribbons manufactured by the conventional method mentioned above are heat-treated under improperly controlled conditions, without causing any enhancement of the magnetic properties, other mechanical defects occur, particularly, the alloys are rendered brittle.
Furthermore, in respect to the defects concerning the product-dimensions of the amorphous alloy ribbons manufactured through the conventional manufacturing methods including the so-called splat cooling step, the products are to be generally formed with a taper in the direction of the widths thereof, and further, rough surfaces are formed. Therefore, due to the inherent manufacturing defects mentioned above, the amorphous alloy ribbons without any heat treatments, or the amorphous alloy ribbons having enhanced magnetic properties through such simple heat treatments as mentioned above, are not available for making specific products in certain technological fields where high precision in manufacturing the products are required, in spite of the fact that the amorphous alloy ribbons might still have quite acceptable magnetic properties.